Causes, seasonality and climate variability of floods in southern Brazil

This is the authors' abstract. We don't add key points for this paper.

Floods, major natural disasters, are shaped by climatic phenomena and regional dynamics. This study explores factors such as event cause, magnitude, seasonality, and the influence of climatic phenomena such as the El Niño Southern Oscillation. The study area is Rio Grande do Sul, southern Brazil, a region that suffers recurrently from floods and faced severe events in 2023 and 2024. The analysis revealed an annual number of 1.6 flood events per station. Excessive rainfall on saturated soils is the primary flood cause, accounting for 67% of events. Larger basins experienced more frequent excessive rainfall floods, while smaller ones were vulnerable to long and short rainfall events. The research revealed no seasonality. El Niño years showed more than twice the frequency of flood events than La Niña and neutral years. The findings align with trends of increasing flood events, emphasizing the need for robust flood risk management strategies in the face of climate change.